Most algae are no longer classified within the Kingdom Plantae.[4][5] The algae comprise several different groups of organisms that produce energy through photosynthesis, each of which arose independently from separate non-photosynthetic ancestors. Most conspicuous among the algae are the seaweeds, multicellular algae that may roughly resemble terrestrial plants, but are classified among the green, red, and brown algae. Each of these algal groups also includes various microscopic and single-celled organisms.

 

 

Hydrilla is a submersed plant that was introduced into Florida as an aquarium plant. Since the 1960s, hydrilla has become the "number 1" aquatic weed in the state, filling lakes and rivers. It has spread rapidly throughout the southern US, and now occurs as far north as Delaware, as far west as California.

by Kenneth A. Langeland
Agronomy Department, Center for Aquatic Plants